Real time measurement of shock pressure

Abstract

A fiber-based optical pressure-sensor, made using semiconductor nanocrystal quantum dots (NQDs) as the active transducing material, provides response time fast enough for shock wave measurements. For NQDs, the shift in band gap as a result of applied pressure can be observed as a shift of the photoluminescence (PL) peak. Further, the shift of the principal absorbance feature allows pressure measurements faster than those obtainable by following the PL peak.

We claim: 
     
       1. A method, comprising:
 positioning nanocrystal quantum dots (NQDs) proximate to an energetic material, 
 compressing said energetic material by detonation whereby a shift in band gap is produced in said NQDs; and 
 observing an electromagnetic product (EMP) of said shift in band gap during compression of said energetic material. 
 
     
     
       2. The method of  claim 1 , wherein observing further comprises producing and transmitting data from said EMP for measuring the amount of pressure within said energetic material. 
     
     
       3. The method of  claim 1 , wherein positioning nanocrystal quantum dots (NQDs) proximate to an energetic material alternatively includes embedding said NQDs within said material. 
     
     
       4. The method of  claim 1 , wherein positioning nanocrystal quantum dots (NQDs) proximate to an energetic material includes abutting a first fiber optic end to a second fiber optic end, wherein said first fiber optic end and said second fiber optic end are embedded within said material, wherein at least one of said first fiber optic end and said second fiber optic comprises a sensing layer comprising said NQDs. 
     
     
       5. The method of  claim 4 , wherein said sensing layer is located between said first fiber optic end and said second fiber optic end. 
     
     
       6. The method of  claim 1 , wherein positioning nanocrystal quantum dots (NQDs) proximate to an energetic material includes abutting a first fiber optic end core to a second fiber optic end core, wherein said first fiber optic end core and said second fiber optic end core are embedded within said material, wherein at least one of said first fiber optic end core and said second fiber optic end core comprises a sensing layer comprising said NQDs. 
     
     
       7. The method of  claim 6 , wherein said sensing layer is located between said first fiber end and said second fiber end. 
     
     
       8. The method of  claim 6 , wherein said sensing layer is coated onto at least one core of said first fiber optic end core and said second fiber optic end core. 
     
     
       9. The method of  claim 3 , further comprising providing a fiber optic splitter comprising an input port, an output port and a return port, wherein said NQDs are operatively attached to said output port, wherein embedding said NQDs within said energetic material includes embedding said output port within said material. 
     
     
       10. The method of  claim 9 , further comprising removing a cladding portion from said fiber optic splitter proximate said output port prior to embedding said NQDs within said energetic material. 
     
     
       11. The method of  claim 1 , wherein said EMP comprises photoluminescence. 
     
     
       12. The method of  claim 1 , wherein said EMP comprises absorbance. 
     
     
       13. The method of  claim 1 , further comprising optically exciting said NQDs. 
     
     
       14. The method of  claim 1 , further comprising optically exciting said NQDs with source selected from a group consisting of a broadband light source and a single wavelength excitation source. 
     
     
       15. The method of  claim 1 , wherein observing an electromagnetic product includes transmitting said EMP to a spectrometer. 
     
     
       16. A method, comprising:
 positioning nanocrystal quantum dots (NQDs) proximate a material, wherein a shift in band gap is produced within said NQDs when said material is compressed; 
 measuring the electromagnetic product (EMP) of said shift in band gap during compression of the material by transmitting said EMP to a spectrometer linked to a streak camera; and 
 producing data from said EMP indicative of the amount of pressure within said material. 
 
     
     
       17. The method of  claim 1 , wherein observing an electromagnetic product includes transmitting said EMP to a spectrometer linked to a detector. 
     
     
       18. The method of  claim 15 , further comprising displaying a spectral intensity of said EMP as a function of time. 
     
     
       19. The method of  claim 16 , wherein said spectrometer spreads said EMP product out in one direction to produce a spread EMP and said streak camera then takes an image of light intensity or a spectrum of said spread EMP and sweeps it in a direction orthogonal to the spread of said spread EMP, so that spectral intensity can be displayed as a function of time. 
     
     
       20. The method of  claim 18 , further comprising capturing an image of said spectral intensity of said EMP as a function of time. 
     
     
       21. The method of  claim 1 , wherein the shift in band gap produced in said NQDs is measured as a shift of the photoluminescence peak which is linearly related to the amount of pressure within the energetic material. 
     
     
       22. An apparatus for sensing pressure, comprising:
 a first fiber optic (FFO) comprising a FFO proximal end and a FFO distal end; 
 nanocrystal quantum dots (NQDs) affixed proximately to said FFO distal end: 
 an electromagnetic radiation source (EMS) for optically exciting said NQDs; 
 means for aligning said EMS into said FFO proximal end; 
 a spectrometer which is operatively aligned with said FFO distal end; and 
 a streak camera which is optically aligned with said spectrometer output for measuring the shift in band gap produced within said NQDs when excited. 
 
     
     
       23. The apparatus of  claim 22 , further comprising a second fiber optic (SFO) comprising a SFO proximal end and a SFO distal end, wherein said SFO proximal end is abutted to said FFO distal end thereby proximately affixing said NQDs to at least one of said FFO distal end and said SFO proximal end, and wherein said spectrometer is operatively aligned to the distal end of said SFO. 
     
     
       24. The apparatus of  claim 23 , wherein said nanocrystal quantum dots (NQDs) are affixed between said FFO distal end and said SFO proximal end. 
     
     
       25. The apparatus of  claim 22 , further comprising a CCD camera, wherein said streak camera is operatively connected and aligned to said CCD camera. 
     
     
       26. The apparatus of  claim 22 , wherein said FFO comprises an unclad core portion proximate said FFO distal end. 
     
     
       27. The apparatus of  claim 23 , wherein said FFO comprises an unclad core portion proximate said FFO distal end and wherein said SFO comprises an unclad core portion proximate said SFO proximal end. 
     
     
       28. An apparatus for sensing pressure, comprising:
 a fiber optic splitter having an input port, an output port and a return port, 
 nanocrystal quantum dots (NQDs) affixed proximately to said output port, 
 a material into which is embedded said output port whereby a shift in band gap is produced in said NQDs by the shock of said material; 
 a light source for directing light into the input port of said fiber optic splitter for exciting the NQDs located at the output port; and 
 a detector located at the return port of said splitter, for receiving emitted light generated at the output port during the shock of said material and, which is coupled back down the fiber from the output port to the return port, for measuring said shift in band gap by filtering out the excitation source light. 
 
     
     
       29. The apparatus of  claim 28 , wherein said fiber optic splitter comprises an unclad core portion proximate said splitter output port for acceptance of an NQD coating. 
     
     
       30. The apparatus of  claim 28 , wherein said detector comprises:
 a spectrometer which is operatively aligned with said splitter return port; and 
 a streak camera which is optically aligned with said spectrometer output for measuring said shift in band gap. 
 
     
     
       31. A method for sensing pressure comprising:
 positioning nanocrystal quantum dots (NQDs) on one unclad end of a single optical fiber proximate to a material, 
 directing a laser light at a wavelength that is absorbed by the NQDs into the opposite end of said optical fiber, 
 producing a shift in absorption frequency in said NQDs when said material is shocked; and 
 optically detecting the variance in light transmitted by said NQDs during shock through the use of a photodiode and oscilloscope. 
 
     
     
       32. The method of  claim 31 , wherein said NQDs comprise PbSe nanocrystal quantum dots.